1. Field of the Invention
The present invention relates to a multiple air-conditioning apparatus having a heat source unit and a plurality of indoor units connected to the heat source unit.
2. Description of the Related Art
In a multiple air-conditioning apparatus wherein a heat source unit is connected to indoor units, the heat source unit comprises a compressor, a four-way valve and a heat-source-side heat exchanger, and each of the indoor units comprises an indoor heat exchanger. The compressor, four-way valve, heat-source-side heat exchanger, and indoor units are successively connected by means of pipes, thereby constituting a heat-pump type refrigerating cycle.
When the compressor is driven and the four-way valve is set in the neutral position, a refrigerant discharged from the compressor flows to the heat-source-side heat exchanger via the four-way valve, and the refrigerant coming out of the heat-source-side heat exchanger returns to the compressor via the indoor heat exchangers and the four-way valve. In this case, the heat-source-side heat exchanger functions as a condenser and the indoor heat exchangers function as evaporators, thereby performing a cooling operation.
When the compressor is driven and the four-way valve is switched, a refrigerant discharged from the compressor flows to the indoor heat exchangers via the four-way valve, and the refrigerant coming out of the indoor heat exchangers returns to the compressor via the heat-source-side heat exchanger and the four-way valve. In this case, the indoor heat exchangers function as condensers and the heat-source-side heat exchanger functions as an evaporator, thereby performing a heating operation.
Examples of the multiple air-conditioning apparatus are disclosed in Published Unexamined Japanese Patent Application (PUJPA) No. 64-6657 and Published Examined Japanese Utility Model Application (PEJUMA) No. 54-685.
PUJPA No. 64-6657 discloses an air-conditioning apparatus wherein indoor units are connected to an outdoor unit. The outdoor unit comprises a compressor, a four-way valve and outdoor heat exchangers, and each of the indoor units comprises an indoor heat exchanger. The compressor, four-way valve, outdoor heat exchangers and indoor heat exchangers are successively connected by means of pipes, thereby constituting a heat-pump type refrigerating cycle. In this air-conditioning apparatus, the capacity of each outdoor heat exchanger is controlled in accordance with the air-conditioning load of each indoor unit.
PEJUMA No. 54-685 discloses an air-conditioning apparatus wherein indoor units are connected to an outdoor unit. The outdoor unit comprises a compressor, a four-way valve and a water heat exchanger, and each indoor unit comprises a heat exchanger. The compressor (1), four-way valve, water heat exchanger and indoor heat exchangers are connected by means of pipes, thereby constituting a heat-pump type refrigerating cycle. In this air-conditioning apparatus, cool water is supplied to the water heat exchanger in the cooling operation mode, and hot water is supplied to the water heat exchanger in the heating operation mode.
In general, the refrigerating cycle is provided with a high-pressure switch which operates at the time of abnormal increase in high-pressure-side pressure. Once the high-pressure switch is operated, the operation of the compressor is stopped, thereby protecting the components of the refrigerating cycle, including the compressor.
The multiple air-conditioning apparatus is provided with two or more indoor units, and the temperature of the refrigerant returning from the indoor units to the heat source unit tends to increase in the cooling operation mode. In particular, when the air-conditioning load of each indoor unit is large, the temperature of the refrigerant sucked in the compressor may reach 40.degree. C. If such high-temperature refrigerant is constantly sucked in the compressor, the compressor may be damaged.
In order to avoid the damage of the compressor, a protection device is provided on the low-pressure-side of the refrigerating cycle. This protection device stops the operation of the compressor when the temperature of the refrigerant sucked in the compressor exceeds a predetermined level for a predetermined time period.
In the meantime, the operation of the high-pressure switch and protection device interrupts the air-conditioning operation, and this is not desirable in maintaining comfortable air-conditioning. It is desirable, therefore, that the high-pressure switch and the protection device be not operated, if possible.